Electrohydraulic metering valves have typically employed solenoids to control the size of a variable aperture in proportion to the magnitude of the signal applied to the solenoid. In some schemes (See, e.g. U.S. Pat. No. 4,585,206 Itoh), the size of the aperture is controlled by application of mechanical force to a metering element, the force being directly applied by an output shaft of the solenoid. Such valves have power requirements that are undesirably high in applications such as single-mission vehicles wherein weight and power economy are key design considerations. Moreover, such valves typically have relatively low metering resolution due to limitations in the practicable stroke of the output shaft. Metering valves have been developed in which fuel flow is controlled by varying the size of an aperture in response to an imbalance of hydraulic forces, wherein the imbalance is effected by changing the input signal to a solenoid (See, e.g. U.S. Pat. No. 4,640,093 Eastman). However, these valves also have high power requirements in comparison to the present invention, one reason being that they require continual application of electrical energy in order to maintain a given flow rate.
Accordingly, an objective of the present invention is to provide a metering valve having low power requirements and relatively high metering resolution. Further objectives and advantages of the invention will be apparent from the following description including the appended claims, when read in conjunction with the accompanying drawing.